The invention relates to a method and an apparatus for the recognition and processing of colors.
The colored images which the invention processes include images or patterns which are to be reproduced, patterns for obtaining control data for textile processing machines, colored printing media, and in general any colored surface or plane.
During trichromatic scanning of colored images, there are produced for each color trichromatic color-measuring signals for the colors red, green and blue, which represent the components of the particular color, or the color-coordinates of the associated color location in the red/gree/blue color space.
In a colored image, there occur fluctuations of the color or changes in color, which, on one hand, are intentional on the part of the designer, but on the other hand may be caused due to color tolerances of colors commercially obtainable, or due to any irregular application of colors. These fluctuations of the individual colors occurred within limited spatial color regions, which are recognized as a color, when determining colors or separating colors, and to which color regions there correspond spatial color recognition regions in the red/green/blue color space.
A color selection circuit then determines continuously, to which of the aforenoted color recognition regions trichromatic color-measuring signals obtained by scanning of the colored image are to be assigned, and which indicate the presence of a color.
Such color selection circuits are used, for example, in color scanners for the manufacture of individual color separators for multi-color printing, or for textile printing, decorative printing or for printing for packing purposes.
When manufacturing color separations for multiple color printing (printing on paper), a color correction is made, which on one hand takes into account any colorwise inadequate quantity of the printing colors, or by means of which any editorially desired color rendition of the reproduction can be changed with respect to the original. In addition to a basic correction, an additional selective correction is made, which only affects certain colors. The problem arises therefore to select with the aid of a color selection circuit only those colors, which must be subjected to a special correction.
Contrary to the multi-printing process, the colors in textile, decorative, or package-printing are mixed prior to printing, and then transferred separately on the printing medium. Here the problem arises to separate the individual colors of the image by means of a color selection circuit from one another, and to obtain a color separation for each color.
A color selection circuit is also needed in a scanner for designed patterns to obtain control data for textile processing machines. Here a similar problem arises, namely to select individual colors from a drawing or pattern having multiple colors. These colors are then converted into control data, and stored on a data carrier as color information.
From U.S. Pat. No. 3,210,552 there has become known a color selection circuit, where the desired boundaries in a color recognition region are formed by electronically adjustable threshold circuits. The apportionment of a color to be identified to the appropriate color recognition region is obtained by comparing the trichromatic color-measuring signals with the suitably adjusted thresholds.
Although the magnitude of the color recognition region is adjustable, it is substantially shaped like a parallelepiped or cube.
The known color selection circuit has a disadvantage, that the shape of the color recognition region cannot be optimally tailored to a color region to be separated, so that errors occur during the color recognition process. It is a further disadvantage, that it is hardly possible, to match the selection circuit to the particularities of the image to be analyzed. The individual adjustment of the thresholds has shown itself to be particularly difficult, for there is no imaginable connection between the color space, on one hand, and the electrical thresholds on the other hand. If a plurality of colors are to be separated, an equal plurality of thresholds or threshold circuits must be used and adjusted, which is very time-consuming and costly.
A variant of the color recognition has become known from U.S. Pat. No. 3,012,666, in which the spatial color recognition is reduced to a two-dimensional problem. The color recognition regions are limited by straight lines, which in turn are simulated by threshold circuits.
In practice it has been shown, however, that even this method does not provide any satisfactory results, as the reliability of the color recognition is often inadequate. There is the additional advantage that as a result of the "banana-like" shape of the color recognition regions, as disclosed in U.S. Pat. No. 3,012,666, it is difficult to fill the whole color space without leaving any gap, with color recognition regions, which in turn also leads to uncertainty during the color recognition process.